medium
6.1
CWE
79
Advisory Published
CVE Published
Updated

CVE-2020-6816: XSS

First published: Tue Mar 24 2020(Updated: )

### Impact A [mutation XSS](https://cure53.de/fp170.pdf) affects users calling `bleach.clean` with all of: * the `svg` or `math` in the allowed/whitelisted tags * an RCDATA tag (see below) in the allowed/whitelisted tags * the keyword argument `strip=False` ### Patches Users are encouraged to upgrade to bleach v3.1.2 or greater. ### Workarounds * modify `bleach.clean` calls to use `strip=True`, or not whitelist `math` or `svg` tags and one or more of the following tags: ``` script noscript style noframes xmp noembed iframe ``` * A strong [Content-Security-Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) without `unsafe-inline` and `unsafe-eval` [`script-src`s](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/script-src)) will also help mitigate the risk. ### References * https://bugzilla.mozilla.org/show_bug.cgi?id=1621692 * https://cure53.de/fp170.pdf * https://nvd.nist.gov/vuln/detail/CVE-2020-6816 * https://www.checkmarx.com/blog/vulnerabilities-discovered-in-mozilla-bleach ### Credits * Reported by [Yaniv Nizry](https://twitter.com/ynizry) from the CxSCA AppSec group at Checkmarx ### For more information If you have any questions or comments about this advisory: * Open an issue at [https://github.com/mozilla/bleach/issues](https://github.com/mozilla/bleach/issues) * Email us at [security@mozilla.org](mailto:security@mozilla.org)

Credit: security@mozilla.org security@mozilla.org

Affected SoftwareAffected VersionHow to fix
pip/bleach<3.1.2
3.1.2
Mozilla Bleach<3.1.2
Fedora=33

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Frequently Asked Questions

  • What is the severity of CVE-2020-6816?

    CVE-2020-6816 is classified as a high severity vulnerability due to its impact on web application security through mutation XSS.

  • How do I fix CVE-2020-6816?

    To fix CVE-2020-6816, you should upgrade the Mozilla Bleach library to version 3.1.2 or later.

  • What software is affected by CVE-2020-6816?

    CVE-2020-6816 impacts Mozilla Bleach versions up to 3.1.2 and Fedora version 33.

  • What types of attacks can CVE-2020-6816 facilitate?

    CVE-2020-6816 can facilitate mutation cross-site scripting (XSS) attacks if improperly handled.

  • Is CVE-2020-6816 applicable to all versions of Mozilla Bleach?

    No, CVE-2020-6816 is specifically applicable to Mozilla Bleach versions lower than 3.1.2.

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